Bidirectional overload clutch



Decn 6, 1949 s w 2,496,172

BI-DIRECTIONAL OVERLOAD CLUTCH Filed April 21, 1945 flaw/M44 1 Patented Dec. 6, 1 949 BIDIRECTIONAL OVERLOAD CLUTCH 'Gunnar Swahnberg, Keene, N. H. Application April 21, 1945, Serial No. 589,579 v 2 Claims. 1

This invention relates to clutches which are effective to transmit torque up to a predetermined ,maximum and then yield whereby to prevent damages to the structures.

A feature of the invention is a clutch mechanism of this type, in which the overload release is effective in either direction of drive.

Another feature is the provision of structural .elements whereby the parts may be assembled for major operation in a selected direction without requiring care in selection and positioning of parts.

. A further feature is the provision of a clutch mechanism which releases upon overload and thereafter permits continued forward motion of 'the driving element without essential drag therequickly reset after on, and which can be easily and overload release.

With these and other features as objects in view, an illustrative embodiment of the invention is shown in the accompanying drawings, in

: which:

Figure 1 is a substantially horizontal section through parts of the rotating knife cage shaft and drive assembly of a lawn mower having the in- 'vention applied thereto.

' Figure 2 is an upright section, substantially on "line 2-2 of Fig. 1, showing the balls and driving cam piece in position for forward drive, and indicating the relative position of the pinion surrounding theseflparts.

Figure 3 is a view corresponding to Fig. 2, with the parts in position for forward release or retrograde drive. Figure 4 is a small sectional view, substantia1ly "on the arcuate line 4-4 of Fig. 3.. Figure 5 is a face view of the shaft driving ring of this illustrative form.

In'the' illustrative form 'of these drawings, the clutch is shown as employed in a lawn mower havthree steel balls 23 each of which is located. in a circular hole 24a of the ball separating and spacing disk 24, this disk being free for movement relative to the shaft II, the ring 20, and the pinion I5.

The pinion I5 has a large central bore to receive a sliding cam piece 25 (Figs. 1 to 4) into the outer edge of which are tightly engaged the equispaced driving pins 26 which extend into apertures in the pinion, and which serve to compel the pinion I 5 and the cam piece 25 to turn-together. V

The cam piece 25 has three equi-spaced arcuately arranged depressions, being one for each of the three balls 23. Each depression (Figs. 2-4) is deeper and wider at its ends 28, 29 than at its mid-length 30, and the fioor therefore slopes toward the mid-length (Fig. 4) to form this shallow part of the respective depression. Thus, each depression is of dumb-bell shape.

A dished spring washer 32 acts between the cam piece 25 and an end nut 33 on the shaft II. Movement of the shaft assembly toward the left .in Fig. 1 is illustrated as prevented by a spacer collar which normally rotates with the shaft II and is fixed against axial movement thereto, to restrict the general axial movement of the shaft II toward the right, and in the description .of operation it will be assumed that only negligible movement of this shaft toward the right can occur.

In operation, as the source of power operates,

. the cam piece 25 is driven, which in the illustrated example is accomplished by the rotation of the ground wheel I3 as the lawn mower travels forwardly, or upwardly in Fig. 1, wherewith the teeth I4 cause the pinion I5 to turn counter-clockwise in Fig. 2, and therewith drive the cam piece 25.

ing a frame I0 which carries the cage shaft I I on 3 the anti-friction bearings I2. This shaft is driven from the ground wheel I3 by engagement of the internal gear teeth I4 thereof with a pinion I5, and thence through the instant clutch. Other on its inner periphery, and has a close sliding fit on the shaft II to permit easy assembly. This shaft has a cross pin 2I which fits the keyways so that the ring and shaft turn together but are permitted relative endwise sliding movements. The ring 20 has a circular groove 22 (Figs. 1 and 5) for receiving clutch elements illustrated as the parts of the lawn mower may be conventional: --the specific form is no part of this invention.

; A ring20 has opposed axial keyways (Fig. 5)

'The balls 23 are in the ends 28 of their respec- 40' lar groove 22 of the ring 20. A load upon the shaft I I, by the cutting of grass or even by the engage- -ment of the knives, causes the balls 23 to act as =wedge pieces between the floors of the depressions tive depressions in this cam piece and in the circuand the ring 20, so that the latter is driven and the cage shaft I I turns. If a greater normal load :;occurs, the ring 20. isretarded by this load and :the continued forward motion of the cam piece,

25 causes the balls to move toward the central part 30 of the respective depressions. This causes an axial separating pressure to be exerted between the ring 20 and the cam piece 25 and the latter moves away against the action of the spring 32 and slides on shaft II. The resistance of this spring against this wedging effect of the balls causes a new equilibrium to be established in which the balls still occupy positions short of the central parts 30 of the depressions. By selection of the slope of the fioors of the depressionswhich preferably are curved to have an increasing slope as the center is approached-and of the pressure of the spring 32, the torque may be transmitted at any load range up to a predetermined maximum, and hence normal cutting of the lawn grass can be effected.

When the mower is pulled backward, the balls 23 pass to the deepest parts 28 of their respective, depressions, the cam piece 25 slides on the shaft I I under the pressure force whichhasbeenstored;

in the spring 32, and the cage remainsstationary as in the conventional lawn mower;

However, if an obstacle such;as a1stump. stone,-.

tree branch, etc., is encountered by the knives.

during forward mowing, movement, the load upon the shaft l I increases beyond this predetermined maximum, and: no positionof equilibrium: is :automatica-lly formed. by the: system, and: the. balls travel past the central parts 30 of the depressions and go to the opposite: ends 29 thereof, in which they no longer can serve as wedges to transmit an effective torque against such: a load;.andithe1 cam piece 25 continues to turn-withouttransmitting its, eifect'to the ring: 29; so thatv the knives--v are quickly relieved from.-driving pressure under the overload, and are saved from extensive damage. Under this conditioner. the parts, the lawn mower is no longer effective for cutting. It can be quickly and easily reset, however, by holding. the shaft H against rotation, asby. blocking the'rotating knife cage against reversedrotation, and

turning the ground wheel l3ba'ckward. The reverse overloading condition is thus established, and the cam piece 25 turns while; ring 29 is blocked, so that the balls are: caused to travel relatively back along-their'respective depressions;

from the ends 29 tothe central parts Sil'and then to the endsZS; The clutch is nowready to drive the knives for cutting again;

The clutch thus can perform: as an overloadrelease clutch during the forward motion and'as:

, and: driving the shaft l l';.usua'l1y after removing the ground wheel. In the present device; the

' same retrograde motion can b'eobitained by blocking the knife cage by an-obst'acle-and causing the balls. totravel. from the ends 28 to the: ends ZQ -as described above. Thus, the: abrasive paste can then be applied totheknives, and thereafter;: by retrograde rotation of the ground: wheel asby backward trundling of the mower along the ground), the cage turns and thegrinding is accomplished. At the conclusion of the grinding, the parts can be cleaned and reset for controlled forward cutting motion as set out above.

While the device has been illustrated with a. lawn mower driven from one end only, it is obvious that it can be employed in many ways where an overload-release or idle-reverse motion is desired. The parts are symmetrical and hence the number of parts to be manufactured or kept in stock for repairs is reduced: and the repairman need not take care to properly insert rights and l'efts..

What is claimed is:

1. An overload clutch comprising coaxial driving and. driven members, said members having a permitted axial movement toward and from one another, means for urging the members together, one said member having an arcuately arranged groovewith its floor sloping from each end toward at shallowpoint between-the ends, the other said member presenting a wall surface substantially in a radial plane opposite said groove, and a torque transmitting device movable along said arcuate groove and engaged with the said wail surface for transmitting" stresses axially between said members, the clutch-acting upon overload to cause the device to travel along the arcuate groove past the'shallow point and therewith causin axial separation of the said'membersagainst the action of said urging means, and tocausethe said device to'pass to the oppositeend' of widercuate groove whereby torelieve the device" from torque transmission upongexcess loading of said driven member.

2. An overload clutch comprisingcoaxialidriving and. driven members, saidmembers. having a permitted axial movement" toward and from one another; a spring for urging the members, together, one" member having a circular groove ini't's end and the other member having at least onearcuate grooveopposed' to said'circular groove said arcuate groove being deeper at its ends. than at the center of its length and havingits floor. sloping toward the center and being symmetrical about the radial plane through said center of length, and a ball engaged in said grooves.whereby the ball acts betweensaidfloor andcthe .walL of the circular groove to transmit driving torque and to approach .the center of 'lengthof thev arcuate groove in proportion as the load increases up to the maximum and therewith forcing the members apart against the, action of the spring,. and whereby said ball passes. beyondlsaidcenter and enters .the other endof' the arcuate groove when said maximum is exceeded;

GUNNAR. SWAHNBER'G'.

REFERENCES CITED" The following references are of? rccordin the file of this patent:

UNITED STATES PATENTS" 5-. Number Name; Date 2,045,086 Kastner J une- 23, 1936 2,182,621 Gauld-, Dec..5, 1939 2,257,759; Niemann Oct. 7,1941 

